The present invention relates to a liquid crystal display apparatus having a novel configuration.
Liquid crystal display apparatuses according to the prior art use a display mode in which an electric field substantially normal to the substrate surface is applied, as typically presented by the twisted nematic (TN) display mode. However, the TN display mode involves the problem of an insufficient viewing angle characteristic.
On the other hand, the In-Plane Switching (IPS) display mode is proposed in JP-B-63-21907, U.S. Pat. No. 4,345,249, WO 91/10936, JP-A-6-160878 and others specifications.
In this IPS display mode, an electrode for driving a liquid crystal is formed one of paired substrates holding the liquid crystal between them, and an electric field having a component parallel to the substrate surface is applied to the liquid crystal. This IPS display mode can provide a wider viewing angle than the TN display mode does.
However, the IPS display mode also involves the problem that the color gray scale varies with the visual angle. In order to solve this problem stated, JP-A-9-258269 or the like specifications among others proposes a multi-domain IPS display mode. A liquid crystal display apparatus using this multi-domain IPS display mode will be described with reference to FIG. 2, FIG. 3 and FIG. 4.
FIG. 2 illustrates the configuration of a liquid crystal display apparatus using a multi-domain IPS display mode. The liquid crystal display apparatus has a signal driver 51 for supplying a signal voltage to each pixel electrode 35, a scanning driver 52 for supplying a voltage for selecting a pixel, a common electrode driver 54 for supplying a voltage to each common electrode 36, and a display control unit 53 for controlling the signal driver 51, the scanning driver 52 and the common electrode driver 54.
The substrate 1 is provided with a plurality of scanning lines 32 connected to the scanning driver 52, signal lines 31 connected to the signal driver 51 and crossing the scanning lines 32, first TFTs 33 arranged in a matching way near the intersections between the scanning lines 32 and the signal lines 31 and electrically connected to the scanning lines 32 and the signal lines 31, the pixel electrodes 35 electrically connected to the first TFTs 33 and matching the signal lines 31, the common electrodes 36 matching the pixel electrodes 35, and electrode connecting portions 36′ electrically connected to the common electrodes 36 and the common electrode driver 54.
A pixel 11 is formed in each area surrounded by signal lines 31 and scanning lines 32, and a plurality of pixels 11 constitute a display section 22.
FIG. 3 illustrates the configuration of a circuit arrangement pattern in a pixel and its vicinity in a liquid crystal display apparatus using a multi-domain IPS display mode. The scanning lines 32 and the signal lines 31 cross each other, and a pixel 11 is formed matching an area surrounded by scanning lines 32 and signal lines 31. Each of the first TFTs 33 is arranged in a matching way near the intersection between a scanning line 32 and a signal line 31, and electrically connected to the scanning line 32, the signal line 31 and the pixel electrode 35. Each of the common electrodes 36 is arranged matching a pixel electrode 35, and the common electrode 36 and the pixel electrode 35 generate an electric field whose components are parallel to the substrate surface. The pixel electrode 35, the common electrode 36 and the signal line 31 are bent once or more within each pixel to constitute a multi-domain. The turning direction of the liquid crystal is reversed in each domain to that in the adjoining domain to expand the visual angle.
FIG. 4 shows an A-A′ section of FIG. 3. This configuration has a substrate 1 made of transparent glass, another substrate 2 arranged opposite the substrate 1 and also made of transparent glass, and a liquid crystal layer 34 held between the substrates 1 and 2. The substrate 1 has a common electrode 36, a signal line 31 arranged in a higher layer than the common electrode 36 with a first insulating film 81 in-between, pixel electrodes 35 matching the common electrode 36 generating an electric field whose components are parallel to the surface of the substrate 1, a protective film 82 provided over the pixel electrodes 35, an alignment film 85 provided over the protective film 82, and a polarizer 6 provided on the other side than the liquid crystal side of the substrate 1 and varying its optical characteristics according to the alignment of the liquid crystal.
The substrate 2 has a light shielding film 5 for shielding against unnecessary lights from gaps; a color filter 4, provided over the light shielding film 5, for expressing colors respectively corresponding to R, G and B; a flattening film 3, provided over the color filter 4, for flattening the unevenness of the filter, an alignment film 85 provided over the flattening film 3, and a polarizer 6 provided over the other side than the liquid crystal side of the substrate 2.
The alignment film 85 is rubbed to align the liquid crystal. The rubbing direction is parallel to the extending direction DLa of the signal line. The angle formed between one side of the bent pixel electrode and the rubbing direction is 15 degrees, matching the IPS display mode. The axis of transmission of the polarizer 6 is either parallel or normal to the rubbing direction of the alignment film on the substrate over which that particular polarizer is arranged, and the polarizer of the substrate 1 and the polarizer of the substrate 2 are in a cross Nicol arrangement, matching the normally black mode.
Picture displaying is accomplished by supplying an electric field whose components are parallel to the substrate 1 onto the liquid crystal 34 with the common electrodes 36 and the pixel electrodes 35 and thereby rotating the liquid crystal 34 in a plane substantially parallel to the substrate 1.